The United Nations General Assembly's annual debate opened in New York Monday with U.S. President Barack Obama and Russian President Vladimir Putin clashing sharply over the Syrian crisis.

President Obama spoke first, calling on the world to shun war and conflict and engage instead in new diplomatic efforts to resolve conflicts across the globe.

“If we cannot work together more effectively, we will all suffer the consequences,” said Mr. Obama. “No matter how powerful our military, how strong our economy, we the United States understand, we cannot solve the world’s problems alone.”

He criticized Russia for helping the Syrian regime and its President Bashar al-Assad and its annexation of Ukraine’s Crimea peninsula and continuing support for pro-Russian separatists in eastern Ukraine, adding western economic sanctions were necessary because no country could overlook the Crimean takeover “with impunity”.

Mr. Obama said there were “no simple answers” to Syria’s crisis but said President Bashar al-Assad should have no role to play in a new Syria.

He said he was willing to work with any country to help resolve the Syrian crisis, adding Mr. Assad was responsible for the creation of the Islamic State insurgents trying to remove him from office.

The American President called for a "managed transition" to oust Mr. Assad adding Syria cannot return to pre-war status quo.

Responding, Russian President Vladimir Putin, who spoke in the morning session as did President Obama, warned that it would be an "enormous mistake" to not cooperate with the Assad government in fighting Islamic State insurgents trying to oust the Syrian leader.

He called for a "broad coalition" to combat Islamic State fighters, much like the "anti-Hitler" alliance that fought together in World War Two. He said there’s no way Assad cannot be part of the solution to the crisis in Syria.

Mr. Putin said aggressive foreign interference in the Middle East and North Africa has resulted in a flagrant destruction of national institutions rather than bringing about reforms, opening the way for tens of thousands of terrorists and extremists to fill the vacuum under the banner of the so-called Islamic State.

“We think it is an enormous mistake to refuse to cooperate with the Syrian Government and its Armed Forces, who are valiantly fighting terrorism face-to-face,” he said, noting the danger posed by foreign Islamic State recruits from Europe and Russia if they returned to their homelands.

“We should finally acknowledge that no one but President (Bashar al-) Assad’s Armed Forces and Kurd militia are truly fighting the Islamic State and other terrorist organizations in Syria.”

Ministerial Meeting

As current President of the Security Council, Russia will convene a ministerial meeting to propose agreement on a resolution to coordinate the actions of all the forces against the Islamic State and other terrorist organizations based on the principles of the UN Charter, he added.

This was Mr. Putin’s first U.N. speech in ten years.

United Nations Golden Ball

Putin warned that many of the crises facing the world today have been exacerbated by countries acting against sovereign States outside the UN Charter.

“We consider the attempts to undermine the authority and legitimacy of the United Nations as extremely dangerous,” he told the General Debate on the opening day of the high-level segment of the Assembly’s 70th annual session.

He cited United States sanctions against Russia over Ukraine as an example and called for full support for the Syrian government in its war against terrorism.

Mr. Putin emphasized the diversity of models among UN Member States and the vital importance of respecting State sovereignty.

“Ensuring peace and regional and global stability remains the key objective of the international community, with the UN at its helm,” Mr. Putin declared. “We believe this means creating a space of equal and indivisible security which is not for the select few, but for everyone.”

This is the 70th session of the United Nations General Assembly

The two presidents spoke ahead of a face-to-face meeting set for later in the day.

President Robert Mugabe is also attending the UN General Assembly in New York.

Political commentator Brilliant Mhlanga said there’s nothing new to expect from President Robert Mugabe’s speech at the UNGA later Monday, adding the 91-year old should stop taking huge entourages to such meetings saying they are draining the fiscus.